Notes from booklet Flashcards
Mass number is what
protons and neutrons
Atomic number is
protons
Tungstan has a K shell energy of what?
69.5keV
What are properties of isotopes
same chemical properties as same protons
How does Iodine 123 decay?
by 160keV Gamma Ray
Isotope vs isotone?
Isotope has same number of protons. Isotone same number of neutrons.
what is a bacquerel?
Number of decays per second
What is emitted with a beta plus decay?
A positron
when a positron and electonr anihilate what is the energy of the resulting photons?
511kEV each
What is emitted in beta minus decay?
electron
EM waves travel in what way?
perpendicular to direction of travel and 90 degrees to each other
what is plancks constant?
the constant connecting Energy and frequency.
relationship of frequency and wavelength
f = 1/ wavelength
equation for contrast
propotional to (u1 - u2) x thickness of material
in CT a reduced FOV and increased matrix size causes what for the noise
smaller pixels, therefore reduced SNR.
in a single slice scanner - does pitch affect the noise?
no, only the spatial resolution due to partial voluming.
in a multislice scanner does pitch incease noise
yes
relationship of SNR and slice width
SNR is proportional to the square root of slice width.
to doulbe your SNR you have to quadruple the slice width.
relationship of SNR and mA
SNR is proportional to the square root of mA
How does windowing affect noise
Decreasing the windowing will increase noise. However the SNR is still the same.
What type of noise is the most significant
Quantum, electronic the least
CT - cupping is the effect of what?
Beam hardening
Ring artefacts are less suceptible in multi or single slice
In multi
XR source to patient distance will affect what
spatial resolution
CTDI depends on what?
mA, kV and filtering.
DLP is what?
CTDI (vol) xL
effective dose and DLP relationship
E = DLP multiplied by the constant for body region and scanner design.
in fluoro - scatter of light in the output window will affect what>
contrast
in fluoro - a single photon will cause how many electrons to be stimulated in the photocathode?
- II input window
Convex metal shield that covers the input face of the II
Usually made of aluminium or titanium foil (low Z metal) to allow x-ray beam to enter with minimum attenuation
Provides protection for sensitive input components of the tube and maintains the vacuum
- Input phosphor
Layer of sodium activated caesium iodide (CsI:Na) for good x-ray absorption efficiency (70-90%)
Channelled into tiny needle-like crystals (5µm in diameter) with fibreoptic-like characteristics
Deposited on a thin aluminium substrate
CsI:Na usually 400-500µm thick
Each x-ray photon produces ~3000 light photons in the blue spectrum
- Photocathode
Fluorescent emission from phosphor then absorbed in a light-activated photocathode comprising a very thin layer of antimony caesium (SbCs3) alloy that has a spectral sensitivity well matched to the blue light emission of CsI:Na
Absorption of the fluorescent light photons releases a pattern of electrons in the body of the II tube
Approximately 200 electrons released per absorbed x-ray photon
what is DQE?
out brightness squared / input signal squared
fluoro - what happens to DAP on magnification
DAP will decrease.
Grid controlled tubes are used in what kind of fluoro
Pulsed mode
in mammography what kind of focal spot size is used
smaller
as the tissue thicness changes in fluoro what happens to the dose rate?
It will stay the same as kV and mA are changed to keep output the same.
in fluoro: what is the quation for minification?
input diameter squared /output diameter squared
Minification gain = (Dinput / Doutput)2 (where D is diameter of input and output screen respectively)
Brightness gain =
minification x flux gain
in fluoro for kids what type of kV do we use?
High kV –> but the resulting image is poorer.
in fluoro - good bone to soft tissue is achieved with high or low kV
low kV
what is the benefit of compression?
it reduces gemoetrical and movement unsharpness
decreased electrons at the edges of the edges of the fluoro II causes increased
distrotion and decreased brightness
in ct: Beam p =
movement / collimation
in Ct: slice p =
movement /slice width
relationship between collimation and slice width
collimation is greater than or equal to slice width.
relationship between slice p and beam pitch. (in ct)
slice p greater than or equal to beam pitch.
in ct what is the spatial resolution
1 / (2 x pixel size)
in ct - what is the pixel size
FOV / matrix
which body is contacted if a high dose is given to a patient
CQC
List some gamma emitters
Tc99m
I 123
Ga 67
In 111
In a fission reactor Uranium becomes what?
Mo99.
in NM imaging - what happens to the image if the collimator has wider holes?
sensitivity goes up
resolution goes down
In NM imaging when is high sensitivity particularly good?
When short frame rate is needed for dynamic studies.
why do we not use a collimator in in PET?
want to increase the sensitivity
T2 is loss of net WHAT magnetisation
transverse
in MRI: relationship between Lamor frequencyt and T
they are proportional. Ie At 1.5T the L is 64 MHz and increases with increasing T.
in MRI - why do lesions have a longer relaxation time
they have a greater content of just water than most tissues.
So a longer T1.
Describe the relationship of T1 loss of magnetisation
Spin lattice - loss to external molecules.
Pure liquid - lots of movement, no time to interact so LONG relaxation
Viscous - less rapid movement, time to interact. Short relaxation.
Solids - the molecules are fixed so can’t interact. Therefore T1 is LONG again .
Describe the T2 loss of coherance
T2, spin spin, loss to each other.
They affect each other - lose coherance.
In liquids - move freely, magnetic field evens out. T2 is long. LONG T2
In solids - can’t move, field is fixed so affects it. Dephase quickly. SHORT T2.
WHich is shorter T2 or T1
T2 is always shorter than T1.
What affect does the Tesla field strength have on T1 and T2
T2 is unaffected (transverse)
T1 timings increase.
US: how long are wavelengths normally
0.1 - 1.5mm
Abdo US frequency
3.5 to 5MHz
How much is reflected from a muslce /bone interface
40%
What is the equation for impedance?
Velocity x density
What is the units of impedance
kg/m-2/s
What are the units of intensity?
W / mm2
What is inensity proportional to?
amplitude squared
resonant frequency is what relation to PZT?
twice the thickness
Damping causes what?
decrease in amplitude
High damping causes what?
decreased amplitude but a wider band of frequencies and a short pulse.
Low damping
higher amplitude, longer pulse.
High Q is which damping - high or low
low
continuous mode has what kind of frequency?
single frequency
pulsed mode is what kind of frequency?
range of frequencies
near field equation is
radius squared / wavelength.
what does the impednace matching layer do
provides further damping in addition to achieving max energy transfer
for a fixed transduceer radius how does the near field change if the frequency is decreased?
decreased.
due to Near field = r squared / wavelength
beam width =
focal length x wavelength
axial resolution =
half the spatial pulse length
lateral resolution =
ultrasound beam width.
which is better - axial or lateral resolution?
axial resolution is better
how does diamter of transducer affect the resolution in the near field
if its a smaller diameter it will be a better resolution in the near field.
What things can change the lateral resolution?
frequency, focusing, transducer diamter, distance from the transducer.
Doppler shift frequency is proportional to
cosine angle of US
what is the maximum doppler shift frequency that can be detected?
PRF / 2
what can a high PRF create?
range ambiguity as echoes are generated generated deeper will be registered as being more superficial.
speed is = to what (relationship of rigidity and density)
= square root of (k/p)
time is
2d / c
Us is what kind of wave?
Longitudinal
How fast are waves?
1540cm/s
the matching layer serves what purpose?
More is transmitted, less is reflected
What is Rayleigh scattering?
When particles are smaller than the size of the wavelength grainy
what is compound imaging?
look behind structures. good fro aorta
What is harmonic imaging?
Non linear propogation of waves to increase resolution
what kind of frequency does the harmonic imaging use?
Higher frequency
Three types of doppler?
Continuous, pusled and colour doppler
Does continous doppler offer depth?
No
Pulsed wave offers what
Depth but lots of alisaing.
What does A, B and M modes mean
A for amplitude - depth of boundaries.
B
M - motion of structures like heart valves.
What temperature rise a risk to the foetus?
1.5 rise
Which is higher energy the pulsed doppler or B mode?
Pulsed doppler
Near field is proportional to what of D
D squared
Lateral resolution is best where? and why?
in the focal zone due to beam narrowing.
pulse length =
number of cycles x wavelength
Q factor equation =
F / bandwith
Intensity reflected =
Z2 - Z1 / Z2 plus Z1 all squared
F doppler
= 2 Ft v cos angle / speed
backscatter is Frequency…..
dependant
doppler is best at what angle
less than 60 degrees due to cosine
does continuous doppler have a velocity limit
no
does pulsed dopper have a velocity limit
yes
what value of MI can cause damage?
> 0.3
What values are disoplayed for MI and TI
if MI greater than 1
if TI is greater than 0.4
In basic sciences - valence band gives what properties
the chemical properties, thermal, optical and electrical properties
what is the speed of EM waves in a vacuum
travels at speed of light
what kind of radiation do you get in Internal conversion?
characteristic radiation as the electrons get replaced.
List some crystals that are used
Silver bromide
Sodium iodide
Caesium iodide
What is a coulomb
1 a / s
what is an eV
it is the energy required to move an electron through one volt.
What happens to the binding energy as the Z increases?
the binding energy increases
how does quantum radiation travel
in a straight line as packets of ernegy
how does the wave aspect of radiation travel
in a transverse waves, sinusoidally varying.
In electromagnetic radiation - travel at…
right angles to each other and the direction of travel.
how does the constant, wavelength and frequency are linked
constant = wavelength x frequency
what is photon fluence?
amount of photons that pass through an area in space multiplied by all their energies
what is energy fluence rate?
it is the photon fluence / second
air kerma
air kerma is measured as a substitute for photon fluence.
equation of air kerma and distance
air kerma B / air kerma point A = distance of A squared / distance of b squared
How do the electrons in the tube lose their energy
Multiple little enrgy losses - heat
large ernegy losses with inner shell or the nucleus.
Why does the energy of the electron need to be greater for higher atomic numbers
What affect does this have on the emitted photons
The nuclear force holding the K shell electron is stronger.
The photons after this interaction are therefore of a higher energy.
Does tube voltage affect the photons emitted from charachteristic interactions?
It does in order for the electron energy to be over the K binding energy. However the energy of the photons will be changed based on the atomic number.
Intensity of the brehmstrauling radiation is proportional to
KV squared x mA (number of electrons)
efficiency of XR production =
XR output / electrical power supplied.
what is the electrical power supplied =
proporitonal to kV x mA
Intensity of XR production
proportional kV squared x mA
interaction of XR with matter - what are the three ways
Transmitted (unaffected), absorbed (lose all their eneregy) and scattered
what is half value thickness?
thickness to reduce by 50%
What is the relationship between LAC and HVL
LAC = 0.693 / HVL
How can you increase the LAC?
increase the density or the atomic number
Intensity of beam equation
I = I E to the pwoer of u d
why do we consider LAC with a thin beam?
the wide beam will have scatter that will give a false higher reading of radiation
Attenutation - low energy or high energy are attenuated more?
Low energy are attenuated more
Which causes is worse for image quality - high energy or low energy beam?
High ernegy - higher energy scatter gets through.
What are the types of attenuation?
Compton (inelastic)
Phtoelectric - TOTAL absorption
Elastic.
In what direction can compton scatter be in?
in all direction
Compton - what direction will the elctron go in?
sideways or forwards (not backwards)
probability of compton is proportional to what?
proportional to physical density (ie mass and electron density)
which has more energy - a forward scattered electron or a side scattered electron?
Forward scattered has more
relationship of compton scatter to density and energy
C = density / E
what is the equation for Photoelectric effect
PE = density x Zcubed / E cubed
describe an absorption edge?
as the energy increase the chances of PE decrease, however when it hits a new electron level the chances suddenly jump up as electrons can be hit from this level.
Which kind of effect, compton or PE, is affected by Z and energy of the photons?
PE is affected most by both.
Compton is NOT related to Z number (only electron density)
PE is more sensitive to energy as it is cubed
sift tusses are affected by compton or PE
compton
heavy stuff is affected by compton or PE
PE (lead ect)
the ionizing path of secondary radiation (within tissues) is what ratio
proprotional to 1 / density
when aluminium is used to filter a beam - what interaction is occurring?
Low energy photons are taken out by the metal through PE interaction.
How much aluminium is used?
2.5mm at 70kv
at diagnostic energies - absorbed dose and air kerma are
the same
how can you improve the quality / intensity of the XR beam?
INcrease the kv
increase mA
intensity proportional to Ma x kV square / Fsquared
which happens quicker phospholuminescence or fluorescence?
Fluoro
what is the usual angle of the anode?
7 - 20 degrees
what type of vapour pressure is desirable for the thermionic emission?
low
high kV will affect scatter how?
increase, more scatter closer to the film
mass attenuation coefficient is what
LAC / density
what are the units of mass attenuation?
cm squared / g
basically LAC per unit of density
why is LAc better than MAC?
describes the depth of tissues rather than the mass
what is LAC?
the fractional reduction in intensity per unit length
units of LAC
mm -1 (per mm)
Total absorption happens in which?
Compton or Photoelectric?
in XR production - what is inherant filtration?
How much is there?
XR passing the tube housing ect
total filter desired is 2.5mm, inherant is 0.5 to 1mm
what is the tube rating?
a high tube rating means it can lose the heat generated efficiently
which type of badge uses a double emulsion film?
Film badges
Beta radiation can travel
a few mm’s
Difference between kerma and absoroption
Kerma - energy transferred
Absoroption - energy absorbed.
.
WHich radiation ionizes directly?
XR and photons?
LET is what
amount of energy transferred in a distance
Relative Radiological Efectiveness is what
ratio of absorbed doses required to produce the same biological end point for two RADIATION types.
Linear no threshold theory exists for which?
Stochastic
radon decays giving out what
Alpha particles
Entrance surface dose can be measured with what?
TLD
Which badge has a linear response over a wide range
TLD
Which has better sensitivity - film or TLD
trick - both the same
most precise dosimeters
electric ones
In MRI the field strength causes what affect on the body
PNS from the gradient coils going on and off
RF pulse will cause what?
Heating
Which is shorter T2 or T2*
T2*, decays quicker due to inhomogeneities
In MRI - what are used to reduce breathing arefacts?
Saturation bands
frequency encoding is done in how many echoes?
one echo
should supervised areas have warning signs
yes
critical examination of installed equipement is usually done by
the installer but also the RPA can do this
Who should be contacted prior to equipement installation
The RPA
who chooses the designated areas?
RPA
Tube leakage from the housing should be what
less than 1 mGy/hr @ 1m
chance of fatal cancer from 1mSv
1 in 20 000
As photon energy increases what happens to attenuation
it decreases
photoelectric effect cause what kind of radiation?
characrteristic
what kind of interaction is an incident energy completely absorbed
photoelectric
describe an Auger electron?
charachteristic radiation is immediately absorbed in LOW atomic number material. This can result in another photoelectron being ejected. This is an auger electron
how does reducing the tube voltage affect side scatter and penetrating scatter?
increase side scatter
reduce penetrating scatter
probaability of compton effect is proportional to what
the density of the material and the electron density
NOT THE ATOMIC NUMBER
what is the atomic number of Tungesten and K shell binding energy?
74 atomic number
K shell is 70
with XR filters, what is the relationship between the peak kV and the absorption edge.
The peak kV should be the right (or the high energy side) of the absorption edge.
the range of secondary electrons is inversely proportional to what
the material density
which has a higher atomic number copper or aluminium?
Copper - greater photoelectric absorption efficiency.
filtration on an xr beam will cause what to the minimum and effective photons?
increase
do photons have mass
no
what kind of filter for xr beam is used in mammography?
malibdium
how do you compensate for having a grid in radiography
photons get absorbed so need more mA across filament to produce more electrons and thereefore more photons.
what is the cost of having a large air gap?
though less noise, also less sharp image.
overcome this by smaller focal spot or bigger focus to object distance.
What does the CT number represent?
The average linear attenuation coefficient in the voxel
what is the HU of white matter?
20 - 30
Partial volume effect:
thin high contrast object at an oblique angle will show as what
it will appear larger.
why is the anod cathode parallel to the z axis
minimise the anode heel effect
what are some features of 4th gen scanners?
larger focus to patient distance - means higher dose needed.
Detectors all the way round - more expensive.
In CT - detectors should have what properties?
fast response, negligible afterglow
wide dynamic range
Solid state detectors are worse than ionization chambers for what one thing?
they are less sensitive.
but smaller and more stable
what are the features of scanograms?
minimal scatter but poor resolution
Radionuclides
why is it that the material from a cyclotron can easily be seperated?
They have different atomic numbers so different physical properites.
Protons are added
do isomers have the smae half life
no
what type of ernegy does beta decay emit?
a continuous spectrum - antineutrino and beta split the enregy in different amounts.
MRI: when is chemical shift used?
fat sat techniques an opposed phase imaging
gradient echo in MRI has what type of weighting?
T2*
MRI: what is the brightness of fat in different PD T1 adnT2
bright in PD and T1. Bright in T2 but not as bright as water.
what causes a low T2 signal?
melanin, calcification, fibrous tissue, high protein content and flow void.
phase encoding direction should be in what direction acorss the imaged object
the shortest
what is the ernst angle?
at this anlge get the miximum the magnetic resonance signal for a given tissue T1. (and at a given TR)
in MRI what is the acquisition matirx normlly?
64 x 64
In STIR - what else in addiiotn to fat is supressed?
Other tissues with similar T1.
- mucoid tissue, haemorrhage, protein rich fluid, gad
melanin (sometimes)
T1 times Mucoid, haemorrhage, protein, melanin.
motion artefacts in MRI occur in what direction?
the phase encoding direction
SNR i sproportional to what of the bandwith in MRI
inversely proportional to the quare root of bandwith
which gives a stronger signal spin echo or gradient?
spin echo. Gradient angle reduces the signal .
what thickness of aluminiium do filters need to be
2.5mm
At the anode - elastic interactoin happens if kV is less than
10eV
At the anode - inelastic interactoin happens in what three ways
heat
characteristic
brehamstrauling
Which of characteristic and brehmstrauling is the most?
Bremstrauling is 80%
what is meant by beam quality?
Ability to penetrate
Beam quanitty means what?
number of photons
What is the angle of deflection in Compton
between straight ahead and down to the angle of deflection.
Is compton coherant or incoherant?
incoherant
if high energy of photon to electron - what kind of angle of deflection of photon occurs
high angle of deflection
What is the compton attenuating coeeficient?
Prob of a compton reaction
What does compton rely on
density of material and electron density.
Apart from hydrogen, in every gram of material there are the same number of
free electrons
Photoelectric interact - what happens to the energy of the photon
completely absorbed
when does the auger electron get released?
Low Z, get complete absorption
equation for PE
p x Zcubed / energy cubed
LAC equation
0.693 / HVl
what is the atomic number of bone
13.8
what is the atomic number of soft tissues
7.4
LAC is combination of
PE and compton
What is the mass energy absorption coefficient MAC =
LAC / density
Benefit of MAC
removes all density, can compare number which relies more on Z
Beam quality equation
kVp + HVL
how does a wider beam affect scatter? and HVL?
higher scatter therefore a misread increased HVL as some of the scatter is registeredas the primary beam.
DQE using SNR equation
DQUE = ( SNR out / SNR in ) asquared
if spatial frequency increases what happens to the MTF
decreases
contrast equation
proprotional to (U1 - U2 ) x thickness
what impact does scatter have on image
reduces contrast
how to overcome scatter
large air gap or scatter grid
MTF of 1 means
range in the image is the same
MTF < 1
lower range in image
MTF = 0
No info in image
Noise relative to signal equation
1 / square root of Number of photons
Noise equation
square root of number of photons
SNR =
N / square root of N
also means just square root of Number of photons
What are the causes of unsharpness
Geometric
image receptor
movement
edge
Geometric unsharpenss happens how?
penumbra
Penumbra is proportional to what
XR focal spot size x Distance of object to film / distance from source to object
plain film radiography - magnification is what?
M = image size / object size = distacne to image from source / distance to object from source
what are units of MAC
cm squared / kg
how can we measure the size of the focal spot?
pin hole imaging
In fluoroscopy the output screen is what material ?
silver activated zinc cadmium sulphide
Where are dynodes used?
Electron multipliers?
Where are focusing electrodes used?
II
What is brightness gain?
ratio of output phosphr brightness to input phosphor brightness
What is the readout of CCD in Fluoro?
30 f/s
What is the normal tube current in fluro?
lower than others, 25Kv
ABC is picked up wher eon the image?
centre of the output screen
vignetting causes what?
magnification at the edges of the film
What happens to SNR after DSA?
SNA goes down as noise is added
How much is the lag in Image intensifiers?
1 ms
Which is better in fluoro - flate plate detectors or image intensifiers with regard to quantum efficieny?
both the same
Why does a grid increase dose in fluoro?
less signal so more dose is given to patient to ensure enough brightness
Which is smaller a photospot camera or a spot film?
photospot is smaller
Continous or pulsed gives better resolution in fluoro?
pulsed
What is the contributer to stray radiation?
scatter from the patient
Operator at 1m gets how much of the dose?
0.1%
Beta rays emit energies in WHAT
a continous spectrum of energy (due to antineutrino)
In US how big are the microbubbles?
1 - 10 micrometeres
doppler shift equation is what
F = 2vF cos0 / c
Us what is the equation of MI
peak rarefractional pressure / square root of frrequency
how can you increase the MI in US
lower the frequency or increase the rarefractional pressure.
What are the three types of pulsed doppler?
Colour
- give a box and direction
Spectral
- sonogram
Power
- good for low flow
Why are the edges of a fluro darker?
vignetting
- less focusing of electrons
- magnified at edges therefore darker image here also
what is the Fluro input energy?
1 miro Gray / second
How much should vignetting be kept below?
below 25%
in fluro - a single photon at the input causes how many electrons and then how many photons?
goes to 3000 electrons
then 100 000 light photons at the output (green)
input phospher is made of what in fluro?
Caesium idodide
in fluro the focus to skin distance is usually
less than 45cm
With regards to MRI and the coils
- Permanent coil offers what?
0.3T
Resistive offers what (MRI coil)
0.5T
What does the faraday cage do in MRI?
protects from external magnetic forces
What is the maximum T to staff limbs?
5T
in CT what is the minimum detectable contrast?
0.5%
Which has a higher CT number contrast or bone?
Contrast
What decides the size of the voxel?
The width of the XR beamm
in CT - what happens to quantum noise as you increase the FOV
the noise decreases
what is CTDI?
the amount of radiation hitting the phantom
CTDIw
accounts for a cylindrical person and beam hardnein.
Middle third
Outside two thirds
CTDIvolume
CTDIw / pitch
Dose legnth product
CTDI vol x ????
what is the atomic number and K edge of Iodine?
Atomic number is 53 and K edge is 33
How big is normal focal spot in radiography?
1mm
How many chambers does an AEC have?
3
critical angle of refraction in Ultrasound
when the refracted beam is parallel to the border
Ultrasound intensity and amplitude are proportional how?
I prop to amp squared
a low kV in film causes scatter to
decrease
what is the minimum dose needed for XR
3 microGray
in radiography - low kV vs high kV and their proportions to the output
in low kV - output is prop to kV CUBED (mammography)
in high kV - output is prop to kV squared
